The present invention relates to a method for allocating and selecting data transmission channels for use between a base station system and a mobile services switching centre in connection with call establishment in a mobile communication system in which a rate adaptation unit is arranged on a data transmission connection between the mobile services switching centre and the base station system, the rate adaptation unit communicating with the base station system via-first data transmission channels and with the mobile services switching centre via second data transmission channels. The invention further relates to a mobile communication system comprising a mobile services switching centre, a base station system, and a rate adaptation unit which communicates with the base station system via first data transmission channels and with the mobile services switching centre via second data transmission channels, and which comprises means for transmitting telecommunication signals associated with a given call between the mobile services switching centre and the base station system.
The present invention relates to call establishment, and particularly to establishing a data transmission connection between a base station system and a mobile services switching centre particularly in a digital mobile communication system in which a rate adaptation unit is arranged between the mobile services switching centre and the base station system.
In the present application, the concept xe2x80x9cbase station systemxe2x80x9d refers to the totality formed by base stations and their control means, i.e. a base station controller. In the present application, the concepts xe2x80x9ccallxe2x80x9d and xe2x80x9ccall establishmentxe2x80x9d refer both to common speech calls and to other telecommunication connections transmitted via a mobile communication network, such as data calls and HSCSD (High Speed Circuit Switched Data) data calls.
The frequency spectrum required by a digital mobile communication system, such as a GSM (Global System for Mobile communications) system, for instance, is dependent on the transfer-rate used on a radio path. The higher the transfer rate used on the radio path, the broader the spectrum needed. Consequently, speech encoding of a fixed PSTN/ISDN (Public Switched Telephone Network/lntegrated Services Digital Network) by which digital encoded data is transmitted 64 kbit/s per each traffic channel, is not usually suitable for use on the radio path. Hence, instead of the speech encoding of the fixed network, RPE-LTP (Regular Pulse Excitationxe2x80x94Long Term Prediction) speech encoding is used on a radio path in the GSM system, for example.
It is thus necessary to provide a rate adaptation unit (transcoder) between a base station system and a mobile services switching centre for adapting, for instance, different data transfer rates to each other. In other words, for instance in the GSM system, transcoder interfaces are 64 kbit/s towards the mobile services switching centre and 8 or 16 kbit/s towards the base station system.
In connection with a common full rate call of the GSM system, the mobile services switching centre allocates for a call an xe2x80x9cAter linexe2x80x9d (16 kbit/s) between the base station system and the transcoder, i.e. a first data transmission channel, and an A interface line (64 kbit/s) between the transcoder and the mobile services switching centre, i.e. a second data transmission channel. In connection with common calls, one Ater line is thus allocated for one A interface line.
The need to produce quicker data transmission connections has led to the fact that the data transfer capacity of a single Ater line between a base station system and a rate adaptation unit is not sufficient. Additional capacity can be provided for instance in connection with an HSCSD data call in such a manner that several Ater lines are allocated for a call, and the Ater lines are combined by utilizing multiplexing and demultiplexing performed at the rate adaptation unit with one A interface line whose data transfer capacity for instance in the GSM system corresponds to the capacity of four Ater lines. The problem then presented is, however, that in a solution of this kind the mobile services switching centre does not always know which Ater lines are already in use, since it only has information on the A interface lines in use. Consequently, it is possible that the mobile services switching centre makes an allocation which leads to a situation in which two calls try to utilize the same Ater line simultaneously.
An object of the present invention is to solve the problem described above by providing a solution for allocating data transmission channels between a base station system and a mobile services switching centre so as to enable the data transfer capacity available to be entirely utilized as flexibly as possible, which solution enables allocation of a single data transmission channel for two calls simultaneously to be avoided. This object can be achieved by the method of the invention, characterized in that the method comprises steps of: storing selection information in the base station system and in the rate adaptation unit on which second data transmission channel the rate adaptation unit should allocate for a call for which a given first data transmission channel or channels are allocated, receiving a message which describes the type of a call to be established from the mobile services switching centre, allocating a number of free first data transmission channels required by the call type, determining by means of the selection information which second data transmission channel the rate adaptation unit selects for use, and transmitting information to the mobile services switching centre about the second data transmission channel the rate adaptation unit will select for use.
The invention further relates to a mobile communication system in which the method of the invention can be utilized. The mobile communication system of the invention is characterized in that the base station system comprises: allocation means which keep a record of the first data transmission channels and which are responsive to a message sent by the mobile services switching centre in connection with call establishment for allocating for said call one or more free first data transmission channels required by the call type of the call to be established, and transmission means which are arranged to send the mobile services switching centre on the basis of information stored in the base station system a message which indicates to the mobile services switching centre which second data transmission channel the rate adaptation unit will select for the call when the allocation means have allocated one or more first data transmission channels for the call.
The invention is based on realizing that allocating and managing data transmission channels between a base station and a mobile services switching centre becomes considerably easier and more flexible when channel allocations are carried out by the base station system. In practice, allocation is performed by a base station controller which is aware of those Ater lines which are free at a given moment. Since information is also stored in the base station controller on which A interface line, i.e. second data transmission channel, a rate adaptation unit selects for the Ater lines selected for use, the base station controller is able to transmit the information on the A interface line to be allocated for the call to the mobile services switching centre. Consequently, it is sufficient that the mobile services switching centre informs the base station controller of the type of the call to be established in connection with call establishment. On the basis of the call type indicated to the base station controller, it is able to infer the number of Ater lines needed and to allocate the necessary free Ater lines, and furthermore, to send a message to the mobile services switching centre to indicate the A interface line via which telecommunication signals associated with the call are transmitted between the rate adaptation unit and the mobile services switching centre.
Hence, the most significant advantages afforded by the solution of the invention are that available data transmission channels can be managed in a simple and flexible manner, that first data transmission channels can be utilized as efficiently as possible, and that second data transmission channels can be successfully managed in all situations independently of the type of a call to be established.
The preferred embodiments of the mobile communication system of the invention are disclosed in the attached independent claims 3 to 5.